RT225 Special Procedures pt 2

• Radiosurgery with modified isocentric linac

• Miniature linac mounted on robotic arm (CyberKnife)

• Miniature linac mounted on CT gantry (Tomotherapy)

Linac-based radiosurgery falls into three main categories:

• Multiple non-coplanar converging arcs

• Dynamic rotation

• Conical rotation

Moving beam techniques with modified isocentric linac

• Basic quality assurance protocols covering the performance of all equipment

• Treatment quality assurance protocols dealing with the calibration and preparation of equipment immediately preceding the radiosurgical treatment

• Treatment quality assurance protocol during the radiosurgical procedure on a patient

Quality assurance protocols for radiosurgery fall into three categories:

• Target localization

• 3D treatment planning

• Radiosurgical delivery of dose

Basic quality assurance protocols covering the performance of all equipment used for:

Mechanical Stability

Neurosurgeons had previous favourable experience with the Gamma Knife, but are concerned about the ___ of linac’s isocentres

Total Body Irradiation (TBI)

A specialized radiotherapeutic technique that delivers to a patient’s whole body a dose uniform to within ±10% of the prescribed dose

Cobalt-60 gamma rays, megavoltage x-rays

In TBI megavoltage photon beams, either ___ or ____ are used

• Irradiation of the whole body

• Half body irradiation

• Total nodal irradiation

In a broader sense, TBI techniques encompass:

• High dose TBI

• Low dose TBI

• Half-body irradiation

• Total nodal irradiation

Categories of TBI depending on clinical situation:

750 - 900 cGy, 200 cGy each in 3 days, 1200 cGy

High dose TBI, with dose delivery in a single session (__ to __ cGy) or in up to six fractions of __ cGy each in __ days (total dose: __ cGy)

10 - 15, 10-15 cGy

Low dose TBI, with dose delivery in __ to __ fractions of __ to __ cGy each

8 Gy

Half-body irradiation, with a dose of __ Gy delievered to the upper or lower half body in a single session

40 Gy, 20 fractions

Total nodal irradiation, with a typical nodal dose of __ Gy delivered in __ fractions

Cytoreductive Conditioning Regimen

TBI is used primarily as part of a preparatory ___ prior to bone marrow transplantation (BMT)

• Patient (autologous transplant)

• Identical Twin (syngeneic transplant)

• Histocompatible donor (allogenic transplant)

BMT source of bone marrow may be:

Chemotherapy, High dose chemotherapy and TBI

Conditioning regiment may be based on ___ alone; however the most common pre-transplant conditioning is a combination of __ and __

Immunosuppression, graft versus host disease

TBI results in ___, which helps prevent the failure of the graft (___ disease)

Pre-transplant conditioning

Before egnraftment of donor bone marrow, ___ is applied to eradicate the tumour cells or cells with genetic disorders

• Various types of leukaemia

• Malignant lymphoma

• Aplastic anaemia

Diseases treated with bone marrow transplantation are:

Ewing’s Sarcoma, Non-Hodgkin’s Lymphoma

High dose TBI has been used as adjuvant therapy in treatment of __ and __

• Lymphocitic Leukaemia

• Lymphoma

• Neuroblastoma

Low dose TBI is used in treatment of:

Total Nodal Irradiation

Is used as adjuvant treatment of autoimmune disease

• Cobalt-60 machines

• Linear accelerators (linacs)

All contemporary TBI techniques use megavoltage photon beams that are produced by:

70×200 cm²

Beams are stationary with field sizes of the order of ___ encompassing the whole patient

Smaller field sizes

Beams are moving, with ___, in some sort of translational or rotational motion to cover the whole patient with the radiation beam

Parallel-opposed irradiations, two equal installments

Usually, ___ are used by delivering each fractional dose in ___ and switching the patient’s position between each

• Dedicated irradiators

• Modified conventional megavoltage radiotherapy equipment

TBI treatments techniques are carried out with:

• Treatment at extended source-surface distance (SSD)

• Treatment at standard SSD after the cobalt-60 machine collimator is removed

• Treatment with a translational beam

• Treatment with a sweeping beam

Modified conventional megavoltage radiotherapy equipment:

Dedicated Irradiators

Treatment machines specially designed for total body irradiation

230cm

In a cobalt 60-machine for TBI, the collimator has been removed to obtain a large field for TBI irradiation at an SSD of ___cm

Dose Prescription Point

TBI dose is prescribed to a point inside the body, referred to as the ___ (usually at the midpoint at the level of the umbilicus)

±10%

TBI procedure must deliver the prescribed dose to the prescription point and should maintain the dose throughout the body within __ of the prescription point dose

Bolus, Partial attenuators, and compensators

Uniformity of dose throughout the body is achieved with the use of __, __, and __

• Absolute beam calibration

• Percentage depth doses or tissue-phantom ratios

• Beam profiles

Basic dosimetric paramterse for TBI are the same as those for standard radiotherapy, including:

Dosimetric parameters

Must be measured under the specific TBI conditions in order to obtain reliable data for clinical use of the TBI

Total Skin Electron Irradiation (TSEI)

A special radiotherapeutic technique that aims to irradiate the patient’s whole skin with the prescribed radiation dose while sparing all other organs from any appreciable radiation dose

Mycosis Fungoides

The choice of electron beams for treatment of generalized skin malignancies (most often ___)

Electron Beams, superficial x-rays

Since the skin is a superficial organ, the choice of ___ for treatment of generalized skin malignancies is obvious, even though ___ were in the past used for this purpose

Electron Linacs

All contemporary TSEI procedures are based on ____ which are used for conventional radiotherapy and modified for delivery of large and uniform electron fields required for the TSEI

Relatively small, relatively complex and cumbersone, major radiotherapy centres

Patient population requiring TSEI is ___ and the TSEI techniques are ___, therefore the TSEI technique is only available in ___